Rhododendrons and azaleas have shallow roots and are easy to transplant. They will not tolerate poor drainage or hot roots. The roots need to be mulched and the urn needs to be placed in such a way the sun doesn't get it hot. The easiest way to do this is to put a liner pot inside the urn with an air space around it to keep the inside pot cool. Also, both pots need drain holes and good drainage.

In the winter, you need special protection since the urn is more exposed to the elements.